Experimental and first-principles investigation of the adsorption and entrapping of guanine with SiO sub(2) clusters of sol-gel silicate material for understanding DNA photodamage

We report a first principles density functional theoretical (DFT) investigation of guanine (G) adsorption onto SiO sub(2) clusters, viz., Si sub(2)O sub(4), Si sub(3)O sub(6), Si sub(4)O sub(8) and Si sub(5)O sub(10) in terms of geometry, binding energy (E sub(B)), binding site, energy gap (E sub(g)), and electronic and spectral properties. Guanine entrapped within a Si sub(9)O sub(18) cluster was also studied in terms of geometry, energy gap (E sub(g)), electronic and spectral properties. We observed that the most stable forms of the cluster were Si sub(5)O sub(10) and Si sub(9)O sub(18). Guanine adsorbed onto SiO sub(2) (G-SiO sub(2)) and guanine entrapped within SiO sub(2) (GE-SiO sub(2)) were analyzed by the B3LYP/LanL2DZ method. The HOMO-LUMO energies illustrate that charge transfer from ligand to metal (L arrow right M) occurs in G-SiO sub(2) clusters as guanine to SiO sub(2). The composite of guanine with nanostructured silica material was prepared by simple precipitation and chemical sol-gel processes. The prepared G-SiO sub(2) and GE-SiO sub(2) composites were characterized by FT-IR and FE-SEM with EDX analysis. The resulting experimental evidence is included for better understanding the guanine adsorption and entrapment. The adsorption and entrapping of G-SiO sub(2) and GE-SiO sub(2) was also confirmed by UV-vis spectroscopy. Experimental results are compared with the DFT results. Furthermore, the sol-gel silicate material used to protect the DNA base (guanine) from UVA-irradiation has been highlighted.